FINAL REPORT

THE EFFECTS OF NATURE TRAILS ON BREEDING BIRDS

Dr . Scott Hickman

Biology Department

College Of Lake County

19351 West Washington

Grayslake, Illinois 60030

INTRODUCTION

The effects of habitat fragmentation on breeding birds

have been well documented (Whitcomb 1977 ; Robbins 1979,

1980 ; Samson 1980 ; Blake and Karr 1984) . Many of our

endangered, threatened and rare forest interior birds have

been found to be area sensitive species which require large

acreages of contiguous habitat for successful nesting . This

finding has been of great importance to designers of nature

preserves and others responsible for nongame habitat

management . However, research to date has not determined

whether or not nature trails constitute habitat

fragmentation for any bird species . If nature trails do

constitute habitat fragmentation they could negatively

affect area sensitive birds two different ways . First, area

sensitive species could be repulsed from the area

immediately surrounding a nature trail because of human

activity or because the trail has altered the geometric

structure of the habitat to the point that it will not be

selected for territory sites . Potentially available habitat

is thereby made unsuitable so that the species' total

reproductive output is lessened . Second, area sensitive

species could suffer greatly decreased reproductive success

in the vicinity of nature trails even if they are not

directly repulsed by them . Many area sensitive species are

area sensitive due to their inability to cope with the

increased predation rates, increased Brown-headed Cowbird

(Molothrus ater) nest parasitism rates, and increased levels

of competition (Stanley Temple p ers . com .) that are

associated with edge habitats (Gates and Gysel 1978) . All

of these problems would also be associated with nature

trails if nature trails constitute edge habitat to edge

preferring species of mammals and birds .

This study investigates the first hypothesis listed

above, that some area sensitive species may be trail

repulsed . It is the simplier of the two hypotheses and it

is therefore logical that it should be investigated first .

This study also investigates the possibility that some bird

species may be trail attracted . Some field ornithologists

have the impression that some species of birds are indeed

attracted to nature trails while other species seem to be

repulsed by them (Dale Birkenholz, p ers . com .) . Other

ornithologists have not noted any such relationship between

2

birds and nature trails (John Fitzpatrick, p ers . com .) .

The determination of whether or not some bird species (or

which bird species) are trail sensitive will provide

critically important information for those responsible for

habitat management and the protection of endangered,

threatened or rare birds .

METHODS

This study was conducted entirely within Lake County,

Illinois .

Dirt, wood chip, or lightly graveled nature

trails (hereafter called test trails) within the woodlands

of Ryerson Conservation Area and Captain Daniel Wright Woods

(Trails i-q in Figs . 1-2) were slowly walked between 05 :30

and 09 :00 hrs . during June, 1985 . Encountered males singing

within approximately 130 m of each side of these test trails

were identified to species and their territories were

mapped . The perpendicular distances from their territory

centroids to the test trails were then determined . The test

trails chosen are approximately 2 m to 3 m wide and

positioned so as to minimize the sampling of habitat

interface edges (Figs . 1-2) . Imaginary trails (hereafter

called control trails) were marked with flagging tape

within trailless sections of MacArthur Woods (Transects a-h

in Fig . 3) . These control trails were also slowly walked a

minimum of 3 times each between 05 :30 and 09 :00 hrs . during

June, 1985 . Encountered males singing within approximately

3

Fig . 1 . Nature trails in Ryerson Conservation Area .

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Fig . 3-* Control "trails" in MacArthur Woods .

130 m of the control trails were sampled as described above

for test trails and the perpendicular distances of their

territory centroids from the control trails were determined .

The censusing of birds surrounding control trails a-d (Fig .

3) was conducted on mornings following the censusing of

Ryerson's test trails (Fig . 1) . The censusing of birds

surrounding control trails e-h (Fig . 3) was conducted on

mornings following the censusing of Captain Daniel Wright

Wood's test trails (Fig . 2) . This daily alternation of

control and test tail censusing was done to minimize error

that might be caused if bird density changed as the breeding

season progressed .

I chose MacArthur Woods as the location for all control

trails because it was impossible to position control trails

within Ryerson or Captain Daniel Wright Woods without

risking the sampling of birds affected by nearby nature

trails . Lake County simply contains no other woods besides

MacArthur that are sufficiently trailless for use as control

sites . Fortunately, the vegetation structure and vegetation

species composition of MacArthur Woods is very similar to

that of both Ryerson and Captain Daniel Wright Woods . All 3

forest preserves are mesic woods bordering the eastern bank

of the DesPlaines River and are in close proximity to one

another in the southern portion of Lake County . For a more

complete description of the vegetation of MacArthur Woods

see Hickman (1982) .

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Repulsion from, or attraction to, nature trails was

determined by comparing the average distance of a species'

territories from test (actual) trails with the average

distance of the same species' territories from control

(imaginary) trails . This comparison was conducted for all

species encountered . Species with territories significantly

closer to test trails than control trails are considered to

be trail attracted . Species with territories significantly

closer to control trails than test trails are considered to

be trail sensitive (repulsed) .

Significant differences

were determined by the MINITAB t-test subprogram (Ryan et

al . 1976) with p< .05 .

RESULTS

Thirtythree species of birds held territories within

130 m of each side of the control and test trails . The

number of territories each of these species held along with

the average distance of each species' territories from

control vs . test trails is shown in Table 1 . Table 1 also

provides the results of the t-tests conducted to determine

whether the difference between the average distance of each

species' territories from control vs . test trails was

statistically significant .

Only 5 species had territories that were significnatly

different in distance from control vs . test trails . Acadian

Flycatcher (Empidonax virescens), Blue Jay (Cyanocitta

8

Table 1 . T-test comparisons of average territory distances fromtest (actual) vs . control (imaginary) trails . N indicatesnumber of territories .

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SPECIES TESTN xd(m) ad

CONTROLN xd(m) ad T Prob.

Red-tailed Hawk 1 30

Red-headed Woodpecker 2 38

Red-bellied Woodpecker 6 70 34 6 47 32 -1 .05 .32

Downy Woodpecker 10 50 34 5 35 15 -1 .13 .28

Hairy Woodpecker 8 53 40 7 45 14 - .52 .62

Northern Flicker 7 51 32 8 67 50 .75 .47

Eastern Wood-Pewee 6 68 60 11 66 53 - .06 .62

Acadian Flycatcher 5 26 14 8 62 27 3 .26 .01

Great Crested Flycatcher 15 40 20 7 63 53 1 .14 .30

Blue Jay 21 46 40 12 89 24 3 .88 .01

Black-capped Chickadee 17 27 27 17 43 39 1 .41 .18

Tufted Titmouse 1 60

White-breasted Nuthatch 10 60 29 10 35 26 -2 .15 .05

Blue-gray Gnatcatcher 1 35

Veery 18 35 26 14 43 28 .82 .42

Wood Thrush 21 63 37 26 58 41 - .43 .67

American Robin 20 15 15 17 68 38 5 .40 .01

Gray Catbird 1 50

Cedar Waxwing 2 37

Yellow-throated Vireo 3 53 35 2 51 49 - .05 .97

Red-eyed Vireo 15 51 34 23 55 41 .34 .70

Cerulean Warbler 4 106

Table 1 . Continued .

10

SPECIES TESTN xd(m) ad

CONTROLN xd(m) ad T Prob .

Ovenbird 10 50 32 25 65 38 1 .2 .24

Kentucky Warbler 1 120

Hooded Warbler 2 31

Scarlet Tanager 11 69 43 14 72 34 .14 .89

Northern Cardinal 13 50 39 11 79 49 1 .58 .13

Rose-breasted Grosbeak 3 40 8 6 37 27 - .25 .81

Indigo Bunting 1 18

Rufous-sided Towhee 1 25 2 60 14

Common Grackle 15 15 15 2 9 9 - .86 .55

Brown-headed Cowbird 8 23 15 10 50 15 3 .96 .01

Northern Oriole 2 29

cristata), American Robin (Turdus migratorius) and

Brown-headed Cowbird all held territories that were

significantly closer to test (actual) than control

(imaginary) trails (Table 1) . White-breasted Nuthatch

(Sitta carolinensis) territories were significantly closer

to control than test trails (Table 1) . The distances of all

other species' territories from control vs . test trails was

not significantly different (Table 1) .

DISCUSSION

I had anticipated that several known area sensitive

species such as Veery (Catharus fuscenscens),

Yellow-throated Vireo (Vireo flavifrons), Acadian

Flycatcher, and the slightly area sensitive Scarlet Tanager

(Piranga olivacea) might be found to be repulsed by nature

trails . But this was not the case (Table 1) . The only

species that had territories significantly closer to control

(imaginary) than test (actual) trails was the White-breasted

Nuthatch (Table 1) and this species does not fit the area

sensitive pattern of being a long distance neotropical

migrant . I remain unsure as to why the White-breasted

Nuthatch should be trail sensitive . It could be possible

that it is repelled by human activity but its presence at

bird feeders makes this seem unlikely . It is possible that

a small, easily noticed bark gleaner such as this nuthatch

would be easy prey for accipiters . A sit and wait predator

1 1

such as an accipiter may preferentially hunt nature trails

due to the increased visibility they afford but I have not

read this in the literature and do not know if this is the

case . The reason for White-breasted Nuthatch sensitivity to

nature trails remains obscure .

The Cerulean Warbler (Dendroica caerulescens) is known

to be area sensitive (Robbins 1979) . This study indicates

that the Cerulean Warbler may also be trail sensitive since

it was only observed along control and not test trail

corridors (Table 1) . However, since only 4 birds were

observed this is light evidence at best and can only be used

to indicate that more study on the response of this species

to nature trails is warranted .

The trail attraction of the Acadian Flycatcher (Table

1) was also surprising . This forest interior species is a

long distance neotropical migrant and was suspected of being

area sensitive by MacClintock et al . (1977) . An Illinois

Natural History Bulletin (1984) reports that John Blake and

James Karr found the critical minimum size of contiguous

forest to be 70 acres for this species which would make it

moderately area sensitive . However, the flycatching habit

of this species requires space for sallying flights which

nature trails provide . I have even seen an Acadian

Flycatcher nest directly over a nature trail at Warren

Woods, Michigan . It is therefore not totally incongruous

12

that this species would be trail attracted even though it is

area sensitive .

The trail attraction of the Blue Jay, American Robin,

and Brown-headed Cowbird (Table 1) was expected . These

species are all recognized as generalists that thrive in

edge or second growth habitats . This study indicates that

trails constitute preferred habitat for these edge species .

Forest interior species did not evolve in close contact

with edge species and, therefore, often do not possess

effective defenses against the problems associated with edge

habitats that edge species cause . Forest interior, area

sensitive species seem excessively susceptible to predation

by Blue Jays and mammals as well as nest parasitism by

Brown-headed Cowbirds (Blake 1983, Whitcomb 1977) . Area

sensitive, forest interior species may also be unable to

effectively handle competition from edge species such as the

American Robin (Stanley Temple p ers . com .) . The attraction

to trails exhibited by Blue Jay, Brown-headed Cowbird, and

American Robin therefore indicates that nature trails

probably cause a decrease in the reproductive success of

forest interior, area sensitive species even though area

sensitive species were not found to be trail repulsed . Area

sensitive birds may be present around nature trails but

their reproductive success in these areas should be in doubt

1 3

since nature trails attract species known to negatively

affect the reproductive success of forest interior birds .

Direct measurement of the reproductive success of birds

along nature trails vs . forest interior regions lacking

trails will have to be conducted to substantiate the extent

to which the reproductive output of areas sensitive birds

may be diminished around nature trails . However, the

accelerating decrease in populations of area sensitive,

forest interior species makes it imperative that individuals

responsible for nongame management and the protection of

endangered, threatened, and rare birds consider the negative

effects on the reproductive success of these birds that

nature trails probably cause . Excessive fragmenting of the

forest interior with nature trails should probably be

avoided .

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LITERATURE CITED

Blake, J .G. 1983 . Trophic structure of bird communities inforest patches in east-central Illinois . Wilson Bulletin95 :416-430 .

Blake, J .G . and J .R . Karr . 1984 . Birds and woodlots .Illinois Natural History Survey Bulletin No . 237 .

Hickman, S . 1982 . Forty-fifth breeding bird census :oak-hickory forest . American Birds 36 :63-64 .

Gates, J .E . and L .W . Gysel . 1978 . Avian nest dispersionand fledgling success in field-forest ecotones . Ecology59 :871-883 .

MacClintock, L ., R .F . Whitcomb, and B .L . Whitcomb .

1977 .Evidence for the value of corridors and minimization ofisolation in preservation of biotic diversity . AmericanBirds 31 :6-16 .

Robbins, C .S . 1979 . Effect of forest fragmentation on birdpopulations . Pp . 198-212 in R .M . DeGraf and K .E . Evans,eds . Management of North Central and Northeastern forestsfor nongame birds . U .S .D .A . Forest Service Gen . Tech . Rept .NC-51 .

Robbins, C .S . 1980 . Effect of forest fragmentation onbreeding bird populations in the Piedmont of theMid-Atlantic Region . Atlantic Naturalist 33 :31-36 .

Samson, F .B . 1980 . Island biogeography and theconservation of nongame birds . Pp . 245-251 in Transactionsof the 45th North American Wildlife and Natural ResourcesConference .

Whitcomb, R .F . 1977 . Island biogeography and "habitatislands" of eastern forest . American Birds 31 :3-5 .

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COLLEGE OF LAKE COUNTY

19351 West Washington StreetGrayslake, Illinois 60030

(312) 223-6601

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